Understanding the Default Lit URP Shader

Oct 13, 2025 by wbrum.org 78 views

Introduction

As a Unity developer, you may have encountered a frustrating issue where the grid in the Editor Scene view appears to be visible through an object with a custom shader. This can be particularly puzzling when you're using a shader that you're certain should be opaque. In this article, we'll explore the reasons behind this phenomenon and provide guidance on how to resolve the issue.

Understanding the Default Lit URP Shader

Before we dive into the custom shader issue, let's take a look at the default Lit URP (Universal Render Pipeline) shader in Unity. The Lit URP shader is a highly optimized and versatile shader that is designed to work seamlessly with the Unity Engine. One of the key features of this shader is its ability to render objects with a high level of detail and realism.

The Magic of the Lit URP Shader

So, what makes the Lit URP shader so special? The answer lies in its use of advanced techniques such as:

Depth Testing: This feature allows the shader to determine whether a pixel is in front of or behind another pixel, effectively creating a 3D representation of the scene.
Stencil Buffer: This feature enables the shader to render objects with a high level of precision and accuracy, even in complex scenes with many overlapping objects.
Alpha Blending: This feature allows the shader to blend pixels with different alpha values, creating a seamless transition between objects.

The Custom Shader Conundrum

Now that we've explored the default Lit URP shader, let's take a look at the custom shader that's causing the grid to appear visible. In this case, we're using a simple shader that's designed to render a basic 3D object. However, when we apply this shader to an object in the Editor Scene view, the grid appears to be visible through it.

Why is the Grid Visible Through My Custom Shader?

There are several reasons why the grid may appear visible through your custom shader:

Lack of Depth Testing: If your custom shader doesn't perform depth testing, it may not be able to accurately determine the depth of pixels in the scene, resulting in the grid appearing visible.
Incorrect Stencil Buffer Settings: If your custom shader doesn't use the stencil buffer correctly, it may not be able to render objects with the desired level of precision and accuracy.
Alpha Blending Issues: If your custom shader doesn't handle alpha blending correctly, it may cause the grid to appear visible.

Resolving the Issue

To resolve the issue of the grid appearing visible through your custom shader, follow these steps:

Check the Shader Code: Review your custom shader code to ensure that it's performing depth testing, using the stencil buffer correctly, and handling alpha blending correctly.
Verify the Shader Settings: Check the shader settings in the Unity Editor to ensure that they're configured correctly for your custom shader.
Test the Shader: Test your custom shader in the Unity Editor to ensure that it's rendering objects correctly and that the grid is not visible.

Example Code: A Simple Shader with Depth Testing

Here's an example of a simple shader that performs depth testing:

Shader "Custom/SimpleShader" {
    Properties {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct appdata {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f {
                float4 vertex : SV_POSITION;
                float2 uv : TEXCOORD0;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            v2f vert (appdata v) {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target {
                fixed4 col = tex2D(_MainTex, i.uv);
                return col;
            }
            ENDCG
        }
    }
    FallBack "Diffuse"
}

In this example, we're using the CGPROGRAM directive to define a custom shader that performs depth testing using the UnityCG.cginc include file. We're also using the Tags directive to specify the render type as opaque, and the LOD directive to specify the level of detail.

Conclusion

In conclusion, the grid appearing visible through your custom shader in Unity can be caused by a variety of factors, including a lack of depth testing, incorrect stencil buffer settings, and alpha blending issues. By following the steps outlined in this article and reviewing your custom shader code, you should be able to resolve the issue and ensure that your shader is rendering objects correctly.

Additional Resources

For more information on Unity shaders and the Lit URP shader, check out the following resources:

Unity Documentation: Shaders
Unity Documentation: Lit URP Shader
Unity Community: Shader Development
Q&A: Why is the Grid Visible Through My Shader in Unity? =====================================================

Introduction

In our previous article, we explored the reasons behind the grid appearing visible through a custom shader in Unity. In this article, we'll answer some of the most frequently asked questions related to this issue.

Q: Why is the grid visible through my shader in the first place?

A: The grid is visible through your shader because the shader is not performing depth testing correctly. Depth testing is a feature that allows the shader to determine whether a pixel is in front of or behind another pixel, effectively creating a 3D representation of the scene.

Q: What is depth testing, and how does it work?

A: Depth testing is a feature that allows the shader to determine the depth of a pixel in the scene. It works by comparing the depth value of a pixel with the depth value of the pixel behind it. If the depth value of the pixel is greater than the depth value of the pixel behind it, the pixel is considered to be in front of the pixel behind it.

Q: How can I enable depth testing in my shader?

A: To enable depth testing in your shader, you need to add the following line of code:

clip(-1);

This line of code tells the shader to clip any pixels that are behind the current pixel, effectively removing them from the scene.

Q: What is the stencil buffer, and how does it work?

A: The stencil buffer is a feature that allows the shader to render objects with a high level of precision and accuracy. It works by storing a stencil value for each pixel in the scene, which can be used to determine whether a pixel should be rendered or not.

Q: How can I use the stencil buffer in my shader?

A: To use the stencil buffer in your shader, you need to add the following line of code:

StencilOp(StencilOpReplace, 1, 0);

This line of code tells the shader to replace the stencil value of any pixel that is behind the current pixel with a value of 1.

Q: What is alpha blending, and how does it work?

A: Alpha blending is a feature that allows the shader to blend pixels with different alpha values, creating a seamless transition between objects. It works by multiplying the alpha value of a pixel with the alpha value of the pixel behind it.

Q: How can I use alpha blending in my shader?

A: To use alpha blending in your shader, you need to add the following line of code:

Blend SrcAlpha OneMinusSrcAlpha;

This line of code tells the shader to blend any pixels that are behind the current pixel with the current pixel, using the alpha value of the current pixel.

Q: Why is my shader not rendering correctly?

A: There are several reasons why your shader may not be rendering correctly. Some common issues include:

Incorrect shader code: Make sure that your shader code is correct and that you are using the correct syntax.
Incorrect shader settings: Make sure that your shader settings are correct and that you are using the correct values.
Incorrect render pipeline: Make sure that you are using the correct render pipeline for your shader.

Q: How can I troubleshoot my shader?

A: To troubleshoot your shader, you can try the following:

Check the shader code: Make sure that your shader code is correct and that you are using the correct syntax.
Check the shader settings: Make sure that your shader settings are correct and that you are using the correct values.
Check the render pipeline: Make sure that you are using the correct render pipeline for your shader.
Use the Unity debugger: Use the Unity debugger to step through your shader code and see where it is going wrong.

Conclusion

In conclusion, the grid appearing visible through your shader in Unity can be caused by a variety of factors, including a lack of depth testing, incorrect stencil buffer settings, and alpha blending issues. By following the steps outlined in this article and reviewing your custom shader code, you should be able to resolve the issue and ensure that your shader is rendering objects correctly.

Additional Resources

For more information on Unity shaders and the Lit URP shader, check out the following resources:

Unity Documentation: Shaders
Unity Documentation: Lit URP Shader
Unity Community: Shader Development